Re: [Qemu-devel] Turning off default storage devices?

[Eric Blake]

On 04/16/2014 09:40 AM, Andy Lutomirski wrote:

>> USB has always been off by default, at least for the boards I'm familiar
>> with, due to the USB emulation's non-trivial CPU use.
>>
>> There's no such thing as a Q35 board without USB in the physical world.
>> Can't stop us from making a virtual one, of course.
>>
>> Likewise, there's no such thing as a Q35 board without AHCI in the
>> physical world, and again that can't stop us from making a virtual one.
>>
>> The difference to USB is that our q35 machines have always had AHCI even
>> with -nodefaults.  You seem to propose adding a switch to disable AHCI,
>> yet leave it enabled with -nodefaults.
>>
>> -nodefaults should give you a board with all the optional components
>> suppressed.
> 
> Will this break libvirt, which may expect -nodefaults to still come
> with an IDE bus?

Libvirt can be taught to deal with whatever default devices are present
vs. mising according to -nodefaults; although the IDEAL situation is
that there would be some QMP command for querying what devices are
present when -nodefaults is used, so that libvirt can reliably supply
all remaining devices.  As long as there is a way to tell between older
qemu that always supplied AHCI and your proposed newer qemu that omits
it for -nodefaults, libvirt should be fine with this proposal.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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